DESCRIPTION: (Adapted From The Investigator s Abstract): Recent studies have provided insights into the transduction of sodium salts and acids by taste receptor cells and the organization of chemical sensitivities in neurons of the afferent gustatory pathway. Information from an amiloride-blockable sodium channel projects into NaCl-best afferent fibers in the chorda tympani nerve and into both NaCl- and sucrose-best neurons in the nucleus of the solitary tract (NST) of the hamster. Human psychophysical studies have shown that this amiloride-sensitive transduction component occurs also in humans but contributes less to the NaCl response than it does in rodents. Blocking this component with amiloride in humans does not reduce the saltiness of NaCl or other salts; rather, it blocks their sour side taste, which is of considerable magnitude for LiCl and Na-gluconate. Adaptation to NaCl, on the other hand, eliminates the saltiness of all salts in human studies and reduces the response of all NaCl-sensitive NST neurons. Studies in this proposal address the relationship between human taste perception, the physiology of the hamster gustatory pathway, and hamster taste receptor mechanisms. The findings will provide a basis for interpretation of adaptation and cross-adaptation effects on hamster NST cells and in human psychophysical studies and will support the overall hypothesis that the cross-adaptation procedure reveals receptor commonalities. tract (NST) of the hamster. Human psychophysical studies have shown that this amiloride-sensitive transduction component occurs also in humans but contributes less to the NaCl response than it does in rodents. Blocking this component with amiloride does not reduce the saltiness of NaCl or other Na+ or Li+ salts; rather it blocks their sour side taste, which is of considerable magnitude for LiCl and Na-gluconate. Adaptation to NaCl, on the other hand, eliminates the saltiness of all salts in human studies and reduces the response of all NaCl-sensitive NST neurons. Studies in this proposal address the relations among human taste perception, the physiology of the hamster gustatory pathway, and hamster taste receptor mechanisms. The first specific aim involves human psychophysical studies that are designed (1) to show that the reported effects of amiloride on saltiness are a result of psychophysical methods that force subjects to combine estimates of separate sensations; (2) to investigate the contribution of an amiloride-sensitive transduction component to the sourness of acids; and (3) to demonstrate reciprocal cross-adaptation effects on the salty taste of NaCl and other Na+ and non-Na+ salts. The second specific aim uses single-neuron recording from the hamster NST to investigate (1) the effects of amiloride on the neural processing of the taste of acids and (2) the reciprocal cross-adaptation effects between NaCl and non-Na+ stimuli. The third specific aim, which will be done in a collaborative effort with Dr. Timothy Gilbertson, uses perforated patch recording from hamster taste receptor cells maintained in an intact epithelium in order to determine (1) whether NaCl-responsive receptor cells also respond to non-Na+ salts and acids, (2) whether continual stimulation with NaCl leads to an adaptive decrease in taste receptor cell excitability that requires a similar time course to recover, and (3) whether adaptation to NaCl reduces the response to any other stimulus that activates the cell, i.e., that adaptation occurs at the whole-cell level. These findings will provide a basis for interpreting adaptation and cross-adaptation effects on hamster NST cells and in human psychophysical studies and will support the overall hypothesis that the cross-adaptation procedure reveals receptor commonalities.